The field of invention is flow promoting material handling conveyances, such as paddles and buckets, and particularly such conveyances which are for handling abrasive fluid (including dry or wet semi-fluid) materials.
Highly abrasive materials which need to be mixed, moved or otherwise handled are encountered in many industries, such as paper and pulp mills and power utilities. These industries engage in transporting and processing highly abrasive materials such as fly ash and wood pulp.
Fly ash is a combustion byproduct from solid fuels, such as coal. The fly ash is an abrasive fine particulate that has multiple commercial uses, but becomes an airborne pollutant if not handled properly. In paper and pulp mills, wood in the form of trees is reduced to a wood pulp that is very abrasive.
Processing the fly ash and wood pulp requires mixing and conveying the highly abrasive material using various means and methods. A known mixing apparatus, such as a pug mill, reduces a coarse substance, such as fly ash, into a pulp. The pugmills mix the fly ash with water to create a pulpy fluid. These mills commonly use mixing paddles to continuously mix and urge the fluid along the length of the pug mill toward an unloading position. Other known methods to convey fly ash or other abrasive materials incorporate buckets mounted on a continuous conveying belt or chain mechanism. The buckets scoop up the abrasive material and dump it at a destination prior to returning for another load.
The highly abrasive fly ash and wood pulp wears away the paddle and bucket material requiring frequent replacement. In addition to the highly abrasive characteristics of the fly ash and wood pulp, the material tends to stick to conventional paddles and buckets reducing their efficiency.
Known paddles and buckets are made of hardened steel which is abrasion resistant. In abrasive environments, such as pugmills and pugmill unloaders handling fly ash, abrasion resistant overlays can be applied to the steel paddles. These paddles are wear resistant, but material sticks to their surfaces, making cleaning difficult.
In order to resolve the sticking problem, paddles and buckets composed of flow promoting materials such as, Ultra High Molecular Weight--Polyethylene (UHMW), nylon, and urethane, have been developed. These materials have a low coefficient of friction which is flow promoting, but at a cost of reduced abrasion resistance. The ends of the paddles or walls moving through the abrasive material constantly wear away requiring paddle replacement.
Conventional methods of bonding abrasion resistant materials to UHMW have been unsuccessful because of the flow promoting properties of the UHMW. In addition, the difference in expansion and contraction characteristics of the UHMW and abrasion resistant materials renders conventional adhesive means unavailable.